But why ? It's not as bad as Sleeping. You can Thaw out.
"A frozen Pokémon can still use the moves Flame Wheel, Sacred Fire, Flare Blitz, Fusion Flare, and Scald while frozen; these moves will thaw the user, thaw the opponent if possible, and deal damage to the opponent" - Bulbapedia.

That's too Under powered with respect to Other Ailments.

Sleep and Poison are too darn OP in my Opinion. Spore, Yawn,Hypnosis,Lovely kiss,Sleep powder,Poison Gas,Toxic, Poison Powder. All these moves have ridiculous accuracy and a very High possibility to inflict Sleep/Poison.

Yeah but the whole thing is freezing can be a side effect, and those moves aren't really... used on most things, with only three p much used competitively even. Just the fact that it can be a side effect has personally left me feeling quite negative about being frozen because it occurs at the worst times.

The others I think are fine, and Toxic/Hypnosis/Sleep Powder tends to miss more often than not when I've been playing really. Plus they're only a side effect from an ability, not really a move, so...